On the presence of a giant bristle worm (Eunice roussaei) IN NW Iberian Peninsula: Comments on its taxonomy and reproductive cycle

Abstract

The presence of a giant “polychaete” annelid of the genus Eunice has been recently recorded in the Ría de Arousa (Galicia, NW Spain). Since Eunice spp. are highly appreciated as bait for recreational fishing in other regions of the world, representing a marine resource of high economic value, this finding may open up a new opportunity for the local bristle worm fishery. The present study aims to gain some insights into the biology of this largely unknown species, gathering information that may contribute to the sustainability and management of this potential fishery. Even though samples could not be collected on a monthly basis as initially planned, our results revealed some interesting features. First, as the taxonomic identity of giant specimens of the genus Eunice has been subject to debate, we used molecular techniques to confirm the identity of the species present in NW Spain. We also sequenced COI–5P in 9 specimens from Vrsar (Istria, Croatia), as well as in one specimen found in the facilities of the Aquarium Finisterrae of A Coruña (NW Spain) in 2015. COI–5P sequences (658 bp) revealed that Galician and Croatian individuals are conspecific and belong to the species Eunice roussaei, previously described in the Mediterranean Sea. Moreover, our data suggest a high haplotypic diversity (18 haplotypes were identified among the 20 sequences analyzed) but a low nucleotide diversity. Second, the observations on the 15 Galician specimens collected between October 2019 and September 2020 suggest that E. roussaei is a dioecious, broadcast spawner that reproduces by releasing free gametes into the water column in the autumn months of November/December. Oocytes maturated from January (mean oocyte size = 105.05 μm) to October (mean oocyte size = 202.02 μm), and oocyte size was positively correlated with water temperature (r = 0.746, p < 0.05), as well as with photoperiod (r = 0.268, p < 0.05).